Passengers flying Frontier Airlines will now have to pay extra to place carry-on bags in the overhead bin or for advance seat assignments.

The move comes as the Denver-based airline tries to transform itself into a fee-dependent airline, similar to Spirit Airlines or Allegiant Air — the only other U.S. carriers to charge such fees.

Frontier says that in exchange for these new fees, it is lowering its base fare by an average of 12 per cent. The new charges apply to tickets purchased on or after Monday.

The fee for using the overhead bin ranges from $20 for frequent fliers who book online to $50 for those who fail to pay before getting to the gate. Most will pay $25 if they check-in online; $35 if they check-in at the airport. Personal items fitting under the seat remains free.

Seat assignments — even for the dreaded middle seat — cost an extra $3 for those who buy while booking online; $8 at check-in. If passengers don’t pay extra, Frontier will assign them whatever seats are leftover.

Frontier is also following the model of other airlines in charging extra for seats with more legroom or just those closer to the front of the plane.

For “select” seats, which are just in the front half of the plane, Frontier will charge an extra $5 to $15 per flight, depending on when they are purchased. “Stretch” seats with an extra 5 to 7 inches of legroom — including those in the exit row — will cost $15 to $50 per flight segment, depending on the distance flown. Connecting passengers would have to pay each fee twice.

Passengers who buy more-expensive, fully-refundable “Classic Plus” fares will get stretch seats for free as well as one checked back and one free carry-on bag. Similar benefits will be given for free to elite members of Frontier’s frequent flier program.

In December, a struggling Frontier was purchased by Indigo Partners LLC, a private equity firm that has revamped several near-bankrupt airlines by changing their business model. One of its latest turnarounds was Spirit, based in Miramar, Fla. Just last week, Frontier named Barry L. Biffle as its new president. Biffle had spent nearly nine year working as chief marking officer of Spirit.

“Frontier is merely copying Spirit, reflecting its investment by Indigo,” said Henry Harteveldt, an airline analyst with Hudson Crossing. “I’m not surprised that the airline is doing this.”